We search for the heavy top (t') quark
pair production decaying to Wq final states
in 760 pb-1 of the CDF Run 2 data sample of
lepton+jets. We reconstruct the mass of the t' quark
and perform a 2D-fit of the observed (HT,Mreco)
distribution to discriminate the new physics signal
from Standard Model backgrounds.

Upper limit, at 95% CL, on the production rate for t'
as a function of t' mass (red).
The purple curve is a theoretical
cross section.
The blue band represents +/-1 standard deviation
expectation limit (light blue corresponds to
+/- 2 standard deviation)

Distributions of HT (left) and Mreco (right)
showing result of the fit for
m(t')=250 GeV.
The normalizations of the various sources
and distortions of kinematic distributions due to systematic effects are
those corresponding to the maximum likelihood when the cross section
for t' is set to its 95% CL upper limit.

2D-distribution of HT and Mreco
of data and simulated physics processes
for m(t')=250 GeV (left) and m(t')=400 GeV (right).
Number of points in scattered distributions of physics processes
correspond to 10 times more data
(100 times more for m(t')=400 GeV ).
Dashed line represent the fitting box.
The ticks at the axes represent the binning used in the fit.
The edge bins are overflow bins and include information outside of the box.

In order to estimate possible excess of events in the tails of
HT and Mreco
we a-priori selected signal box (the area outside of dashed region
in the left plot)
with ~ 1% of SM events.
We expect 6.8 events from SM processes, and observe 7.
We also use our likelihood as a goodness-of-fit by drawing
pseuodexperiments from SM distributions.
We obtain that 31% of pseudoexperiments are less likely than data.